Flexible pipe

ABSTRACT

The formation of a resin layer, a metal layer and an insulating resin layer on an outer surface of a corrugated metal pipe for flowing a fluid provides a flexible pipe, whose corrugated metal pipe does not suffer from having apertures even with spark discharge by induced lightning.

FIELD OF THE INVENTION

The present invention relates to a flexible pipe for fluids such as gas,water, etc. which is installed in the walls or under the floors ofbuildings, etc., particularly to a flexible pipe having a safety measureto induced lightning caused by lightening, etc.

BACKGROUND OF THE INVENTION

Recently, flexible pipes are widely used in piping in buildings, etc.for fluids such as gas, water, etc. As shown in FIG. 7, a flexible pipegenerally used is produced by corrugating a hoop sheet of stainlesssteel having a thickness of about 0.2-0.5 mm, and forming a soft vinylchloride resin layer 4 having a thickness of about 0.5-1 mm on the outersurface of the resultant bendable corrugated metal pipe 2.

When lightening hits near a building, large current of lighteningintrudes into the building through conductors such as the ground, thesteel frames of the building, electric wires, etc. This phenomenon iscalled “induced lightning.” Although the corrugated metal pipe isusually grounded or kept at potential extremely close to the groundpotential, the induced lightning intruding into the building causesspark discharge, for instance, between the steel frames of the buildingand the corrugated metal pipe installed nearby, so that apertures ofabout 1 mm in diameter are likely to be formed in the corrugated metalpipe 2.

Various attempts have been proposed to provide safety measures forflexible pipes to the induced lightning. JP2002-174374A proposes alightening-resistant pipe comprising a conductive coating layer formedon an outer surface of a flexible metal pipe, the conductive coatinglayer being conductively connectable to external conductive facilities.JP2003-083483A proposes a lightening-resistant pipe comprising aflexible metal pipe, and an insulating coating layer formed on the outersurface of the flexible metal pipe, the insulating coating layer beingprovided on its inner surface with longitudinal grooves and a conductivecoating layer in contact with the flexible metal pipe, and theconductive coating layer being conductively connectable to externalconductive facilities. JP2002-310381A proposes a piping comprising ametal pipe, and a self-fusible, insulating tape made of anethylene-propylene rubber as a main material and having a thickness of0.5-0.8 mm, which is wound around the metal pipe to prevent damage byinduced lightning. JP2002-315170A proposes a piping comprising a metalpipe, and a self-fusible, insulating tape made of an ethylene-propylenerubber as a main material and wound around the metal pipe, and agrounded, shielding metal layer provided on the self-fusible, insulatingtape, to prevent damage by induced lightning. JP2003-083482A proposes alightening-resistant pipe comprising a flexible metal pipe, aninsulating coating layer formed on the outer surface of the flexiblemetal pipe, and a wire- or strip-shaped conductive member integrallyprovided on the inner or outer surface of the insulating coating layer,the conductive member being conductively connectable to externalconductive facilities.

It has been found, however, that the formation of a conductive coatinglayer on the outer surface of a corrugated metal pipe as described inJP2002-174374A, JP2003-083483A and JP2003-083482A, and the winding of aself-fusible insulating tape around the metal pipe as described inJP2002-310381A and JP2002-315170A are insufficient as safety measures tothe induced lightning.

It is not easy to completely insulate the corrugated metal pipe, andattempts to secure insulation to the spark discharge make the insulatinglayer too thick, resulting in providing the flexible pipe with reducedflexibility, disadvantageous for piping. It also enlarges the outerdiameter of the flexible pipe, thereby needing large joints to beconnected.

OBJECTS OF THE INVENTION

Accordingly, an object of the present invention is to provide a flexiblepipe sufficiently protecting a corrugated metal pipe from inducedlightning.

Another object of the present invention is to provide a flexible pipecomprising a conductive layer near a corrugated metal pipe, theconductive layer being closer to a ground potential than the corrugatedmetal pipe, so that lightening current generated in the flexible pipe byspark discharge due to large potential difference in the building canescape to the ground through this conductive layer, to prevent directdischarge and damage to the corrugated metal pipe.

DISCLOSURE OF THE INVENTION

The flexible pipe according to one embodiment of the present inventioncomprises a resin layer and a conductive coating layer in this orderfrom below on an outer surface of a corrugated metal pipe for flowing afluid. Even with spark discharge occurring in the flexible pipe byinduced lightning, this coating structure protects the corrugated metalpipe from having apertures, thereby preventing gas leak, etc.

Both of the resin layer and the conductive coating layer preferablycovers the entire outer surface of the corrugated metal pipe. The resinlayer may be a conductive layer or an insulating layer. The resin layerand the conductive coating layer are preferably formed in this orderfrom below on the outer surface of the corrugated metal pipe. Theconductive coating layer is preferably made of a metal.

The resin layer preferably covers the entire outer surface of thecorrugated metal pipe, and the conductive coating layer is preferablyconstituted by at least one metal tape extending along the corrugatedmetal pipe.

The flexible pipe according to another embodiment of the presentinvention comprises a first resin layer, a conductive metal layer, and asecond resin layer in this order from below on an outer surface of acorrugated metal pipe for flowing a fluid. Even with spark dischargeoccurring in the flexible pipe by induced lightning, this coatingstructure protects the corrugated metal pipe from having apertures,thereby preventing gas leak, etc.

The first and second resin layers may be conductive layers or insulatinglayers. Accordingly, the coating layer structure on the corrugated metalpipe may be (a) an insulating resin layer, a metal layer and aninsulating resin layer, (b) a conductive resin layer, a metal layer andan insulating resin layer, (c) an insulating resin layer, a metal layerand a conductive resin layer, or (d) a conductive resin layer, a metallayer and a conductive resin layer, in this order from below. Tocompletely prevent lightening current from flowing through thecorrugated metal pipe, the layer structures (a) and (c) are preferable,and the layer structure (a) is particularly preferable.

The metal layer is preferably constituted by at least one metal tapeextending along the corrugated metal pipe. The metal layer may be formedby a metal foil, woven or knit metal wires, a vapor-deposited,conductive layer or a metal plating, in addition to the metal tape. Theconductive resin layer may be obtained by blending fine conductorparticles such as metal powder, carbon black, carbon fibers, etc. withhighly flexible resins such as rubbers, vinyl chloride resins, etc., butmay be formed by a conductive paint containing fine conductiveparticles.

The flexible pipe according to a further embodiment of the presentinvention comprises a corrugated metal pipe for flowing a fluid, a firstinsulating resin layer covering the entire outer surface of thecorrugated metal pipe, pluralities of metal tapes longitudinallyextending on the outer surface of the first insulating resin layer, anda second insulating resin layer covering the entire outer surface of thefirst insulating resin layer via the metal tape, the first and secondinsulating resin layers being easily peelable. With this structure, (a)lightening current is completely prevented from flowing through thecorrugated metal pipe, and (b) the metal tape can be easily removed bypeeling the second insulating resin layer.

The first and second insulating resin layers are preferably formed by anextrusion lamination method, and not thermally fused. A parting layermay be provided between the first and second insulating resin layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a cross-sectional view showing a flexible pipe according tothe first embodiment of the present invention.

FIG. 1(b) is a cross-sectional view taken along the line A-A in FIG.1(a).

FIG. 2(a) is a perspective view showing one example of flexible pipesaccording to the second embodiment of the present invention.

FIG. 2(b) is a cross-sectional view taken along the line B-B in FIG.2(a).

FIG. 3(a) is a perspective view showing another example of flexiblepipes according to the second embodiment of the present invention.

FIG. 3(b) is a cross-sectional view taken along the line C-C in FIG.3(a).

FIG. 4(a) is a cross-sectional view showing a flexible pipe according tothe third embodiment of the present invention.

FIG. 4(b) is a cross-sectional view taken along the line D-D in FIG.4(a).

FIG. 5 is an enlarged view of part of FIG. 4(a).

FIG. 6 is a partially broken perspective view showing the flexible pipeof FIG. 4.

FIG. 7 is a cross-sectional view showing a conventional flexible pipe.

DESCRIPTION OF THE BEST MODE OF THE INVENTION

The flexible pipes in embodiments of the present invention will beexplained in detail below referring to the attached drawings. Unlessotherwise mentioned, the explanation of each embodiment is applicable tothe other embodiments. Also, numerical values appearing in eachembodiment are mere examples without restrictive intension. Further, toclarify features appearing in the drawings, the thickness of metallayers is exaggerated in each figure.

First Embodiment

FIGS. 1(a) and 1(b) show a flexible pipe according to the firstembodiment of the present invention. The flexible pipe in the firstembodiment comprises a resin layer 14 and a conductive coating layer 16formed in this order on the entire outer surface of a corrugated metalpipe 12 having the same structure as that of the conventional corrugatedmetal pipe 2 shown in FIG. 7. The resin layer 14 is preferably ahigh-insulation, soft vinyl chloride resin layer having a thickness ofabout 0.5-1 mm, but it may be a conductive resin layer. The conductiveresin layer may be obtained by blending highly flexible resins such asrubbers or vinyl chloride resins, etc. with fine conductor particlessuch as metal powder, carbon black, carbon fibers, etc. The resin layer14 may be formed by an extrusion lamination method.

The conductive coating layer 16 is preferably made of high-conductivitymetals such as copper, aluminum, etc., but it may be formed by aconductive paint having slightly lower conductivity. The conductivepaint can be applied by spraying, brushing, etc. The flexible pipe 12and the conductive coating layer 16 are grounded.

The experiment of applying predetermined voltage to the resultantflexible pipe to cause spark discharge indicated that no apertures wereformed in the flexible pipe at all despite that spark discharge occurredin the corrugated metal pipe 12, confirming that the flexible pipe hadexcellent induced lightning resistance.

For comparison, a flexible pipe comprising a conductive coating layer 16and an insulating resin 14 formed in this order on the entire outersurface of the corrugated metal pipe 12, just opposite to the layerstructure of the first embodiment, and a flexible pipe comprising aconductive paint layer and an insulating resin layer 14 formed in thisorder on the entire outer surface of the corrugated metal pipe 12 wereproduced, and subjected to the same experiment of induced lightningresistance. As a result, it was found that apertures having diameters ofabout 0.2-1.5 mm were formed in the corrugated metal pipes 12 in bothflexible pipes. This verifies that to improve the induced lightningresistance, the conductive coating layer 16 should be formed over theresin layer 14. It is presumed that why apertures are formed in thecorrugated metal pipe 12 in a case where the outermost layer is aninsulating resin layer is due to the fact that large electric charge isstored partially in the insulating resin layer at the time of sparkdischarge.

Second Embodiment

The outermost conductive coating layer 16 need not cover the entireouter surface of the corrugated metal pipe 12, but may be partiallyformed on the resin layer 14. In examples shown in FIGS. 2 and 3, theconductive coating layer 16 is constituted by pluralities oflongitudinally extending conductive tapes, which partially cover theresin layer 14 formed on the entire outer surface. The conductivecoating layer 16 is constituted by two conductive tapes disposed at acircumferential interval of 180° in the example shown in FIG. 2, and byfour conductive tapes disposed at a circumferential interval of 90° inthe example shown in FIG. 3. The conductive tape is preferably a metaltape of about 10 mm in width and about 0.02-0.1 mm in thickness, such asa metal foil tape of copper, etc., for instance, when the corrugatedmetal pipe 12 has a diameter of about 15-28 mm.

The use of pluralities of metal tapes is to provide the flexible pipewith improved reliability in induced lightning resistance, taking intoconsideration the likelihood that one metal tape is burned out by onelightening, although one metal tape can exhibit enough induced lightningresistance as long as it meets the conditions of current resistance andresistivity. The arrangement of pluralities of metal tapes makes it easyfor discharge to occur between the metal tapes with narrow gaps, surelyproviding lightening current path. In an arbitrarily bendable flexiblepipe, metal tapes tend to be broken on the outside surfaces of its bentportions, but they permit electric current to flow not only through thebroken portions but also between adjacent ones by discharge, so thatlightening current can surely escape to the ground.

The flexible pipe in the second embodiment may be the same as theflexible pipe in the first embodiment except for the conductive coatinglayer 16. Accordingly, the resin layer 14 may be a conductive resinlayer.

The same experiment of induced lightning resistance as in the firstembodiment was conducted on the flexible pipe in the second embodiment,revealing that no apertures were formed at all in the corrugated metalpipe 12.

Third Embodiment

FIGS. 4-6 show a flexible pipe according to the third embodiment of thepresent invention. This flexible pipe has a three-layer coatingcomprising a first resin layer 20, a conductive metal layer 22 and asecond resin layer 24 on the entire outer surface of a corrugated metalpipe 12. The first and second resin layers 20, 24 may be conductive orinsulating. The second resin layer 24 protects the metal layer 22 fromcorrosion, thereby preventing the metal layer 22 from peeling by anexternal force (for instance, bending force) during installation. Theconductive resin layer may be the same as described above. Theinsulating resin layer may be a high-insulation, soft vinyl chloridelayer having a thickness of about 0.5-1 mm like as in the firstembodiment. The metal layer 22 is grounded. Both first and second resinlayers 20, 24 may be formed by an extrusion lamination method.

Accordingly, the coating layer may have a structure of (a) an insulatingresin layer, a metal layer and an insulating resin layer, (b) aconductive resin layer, a metal layer and an insulating resin layer, (c)an insulating resin layer, a metal layer and a conductive resin layer,or (d) a conductive resin layer, a metal layer and a conductive resinlayer, in this order from below. Because the conductive resin layer hasmuch higher electric resistance than that of the metal layer, theinduced lightning resistance is not affected by whether or not theinnermost layer is a conductive resin layer or an insulating resinlayer. However, to surely prevent lightening current from flowingthrough the corrugated metal pipe, the layer structures (a) and (c) arepreferable, and the layer structure (a) is most preferable.

The metal layer 22 is preferably formed by a high-conductive metal foilof aluminum, copper, etc. A tape-shaped metal foil preferably extends ina longitudinal direction on or wound by at least one turn around theouter surface of the first resin layer 20. Alternatively, a metal tapewith an adhesive on the rear surface may be attached to the outersurface of the first resin layer 20, but it had better not be bonded tothe outer surface of the first resin layer 20 such that it can be easilypeeled at the time of recycling.

Like in the second embodiment, the metal layer 22 need not be formed onthe entire outer surface of the corrugated metal pipe 12, and it may beformed by pluralities of tape-shaped metal foils (metal tapes) as longas they meet the conditions of current resistance and resistivity.Because lightening current flows to the ground through the metal layer22 when hit by lightening, the larger thickness and width the metal foilhas, the higher lightening current resistance it has. The experiment ofcausing spark discharge in a flexible pipe provided with one copper foilof 35 μm in thickness and 5 mm in width as the metal layer 22 confirmedthat it withstood at least one impulse current of 8/20 μS having a peakcurrent value of 30 kA.

When the metal layer 22 is made of copper, aluminum, etc., it may bebroken when the flexible pipe is bent, because of no extendibility.However, because the flexible pipe has an insulating resin layer 24 asan outermost protective layer, the peeling of the metal layer 22 isprevented. Unless the metal layer 22 peels completely, its lighteningresistance is not lost to such high current as to cause damage to theflexible pipe, even though it is broken to some extent, becausedischarge easily takes place in gaps in the broken portions of the metallayer 22. Even with gaps of 10-30 mm longitudinally at 1-meter intervalsin metal foils, the metal foils' induced lightning resistance was notreduced.

What is necessary to form this three-layer coating is only to form thefirst resin layer 20 on the outer surface of the corrugated metal pipe12, attach the metal layer 22 constituted, for instance, by tape-shapedmetal foils, and then form the second resin layer 24 thereon. The metallayer 22 sandwiched by the first resin layer 20 and the second resinlayer 24 is preferably easily peelable from any layer, to make recyclingeasy. For this purpose, it is preferable to form a parting layer on themetal layer 22 in advance.

As a result of conducting the same experiment of induced lightningresistance as in the first embodiment on the flexible pipe in the thirdembodiment, no apertures were formed at all in the corrugated metal pipe12.

Specifically, the flexible pipe in the third embodiment comprises acorrugated metal pipe 12 for flowing a fluid, a first insulating resinlayer 20 covering the entire outer surface of the corrugated metal pipe12, pluralities of metal tapes 22 longitudinally extending on the outersurface of the first insulating resin layer 20, and a second insulatingresin layer 24 covering the entire outer surface of the first insulatingresin layer 20 via the metal tape 22, the first and second insulatingresin layers 20, 24 being easily peelable.

As described above, when the first and second insulating resin layers20, 24 are formed by an extrusion lamination method, both layers 20, 24are likely to be thermally fused if they are made of the same resin. Ifthe first and second insulating resin layers 20, 24 were thermallyfused, it would be difficult to remove the metal tape 22 at the time ofrecycling. Accordingly, lest that the first and second insulating resinlayers 20, 24 are thermally fused, a parting layer is preferablyprovided between both layers. The parting layer is preferably made of asilicone resin, etc.

To make the removal of the metal tape 22 easy at the time of recycling,the metal tape 22 are preferably coated with a parting layer asdescribed above. When the second resin layer 24 is extrusion-laminatedto the metal tape 22 coated with a parting layer, which are laid on thefirst resin layer 20 coated with a parting layer, the second resin layer24 is neither thermally fused to the first resin layer 20 nor to themetal tape 22. Accordingly, the metal tape 22 can be easily removed bycutting the second resin layer 24 by a cutter, etc.

In all embodiments, the metal layer should have lower electricresistance per unit length than that of the corrugated metal pipe, suchthat electric current flows predominantly in the metal layer than in thecorrugated metal pipe. The metal layer may be in the form of a tape ortube formed by woven or knit conductive metal wires, a vapor-deposited,conductive layer or a metal plating, in addition to the metal foil.

EFFECT OF THE INVENTION

Because the flexible pipe of the present invention comprises a resinlayer and a metal layer on an outer surface of a corrugated metal pipe,no apertures are formed in the corrugated metal pipe even with sparkdischarge occurring in the flexible pipe by induced lightning, therebypreventing gas leak, etc. Also, because it can be provided with improvedspark discharge resistance (induced lightning resistance) withoutincreasing the thickness of the resin layer, the flexible pipe does notsuffer increase in an outer diameter and decrease in flexibility.

With a coating layer structure on the outer surface of the corrugatedmetal pipe comprising a first insulating resin layer, pluralities ofmetal tapes and a second insulating resin layer, (a) lightening currentis completely prevented from flowing through the corrugated metal pipe,and (b) the metal tapes can be easily removed by peeling the secondinsulating resin layer, thereby making recycling easy.

What is claimed is:
 1. A flexible pipe comprising a first resin layer, aconductive metal layer and a second resin layer in this order from belowon an outer surface of a corrugated metal pipe for flowing a fluid,wherein said metal layer is constituted by at least one metal tapeextending substantially parallel to the longitudinal axis of saidcorrugated metal pipe, and wherein said first resin layer and saidsecond resin layer are laminated partly in contact with each other. 2.The flexible pipe according to claim 1, wherein said conductive coatinglayer is made of a metal.
 3. The flexible pipe according to claim 1,wherein both of said resin layer and said conductive coating layer coverthe entire outer surface of said corrugated metal pipe.
 4. The flexiblepipe according to claim 1, wherein said first and second resin layersare conductive layers or insulating layers.
 5. The flexible pipeaccording to claim 4, wherein said conductive resin layer is formed by aconductive paint.
 6. The flexible pipe according to claim 1, whereinsaid metal layer is formed by a metal foil, woven or knit metal wires, avapor-deposited, conductive layer, or a metal plating.
 7. The flexiblepipe according to claim 1, wherein said metal tape longitudinally hasgaps in broken portions.
 8. The flexible pipe according to claim 7,wherein a thickness of said metal tape is 0.02-0.1 mm.
 9. The flexiblepipe according to claim 1, wherein said first resin layer and saidsecond resin layer are not peelable.
 10. A flexible pipe comprising acorrugated metal pipe for flowing a fluid, a first insulating resinlayer covering the entire outer surface of said corrugated metal pipe,at least one metal tape extending substantially parallel to thelongitudinal axis of said corrugated metal pipe on the outer surface ofsaid first insulating resin layer, and a second insulating resin layercovering the entire outer surface of said first insulating resin layervia said metal tape, said first and second insulating resin layers beinglaminated partly in contact with each other but easily peelable.
 11. Theflexible pipe according to claim 10, wherein said first and secondinsulating resin layers are formed by an extrusion lamination method,and not thermally fused.
 12. The flexible pipe according to claim 10,comprising a parting layer between said first and second insulatingresin layers.